N-way power divider with remote isolating resistors

ABSTRACT

Disclosed is an isolated N-way power divider for operation at high frequencies. The power divider has isolating resistive terminations in the form of transmission line terminations connected to a set of transmission lines. The termination and transmission line arrangement eliminates the need for a set of &#39;&#39;&#39;&#39;star connected&#39;&#39;&#39;&#39; resistors characteristic of prior art isolated power dividers.

United States Patent [191 LaRosa Sept. 9, 1975 N-WAY POWER DIVIDER WITH REMOTE ISOLATING RESISTORS [75] Inventor: Richard La Rosa, South Hempstead,

[73] Assignee: Hazeltine Corporation, Greenlawn,

[22] Filed: June 7, 1974 [21] Appl No.: 477,389

(52] U.S. Cl. 333/9; 333/84 M [St] Int. Cl. H01? 5/l2 [58] Field of Search 333/6. 8, 9, ll

[56] References Cited UNITED STATES PATENTS 3,529,265 9/1970 Podcll 333/9 Primary Exuminer-Paul L. Gensler [57] ABSTRACT Disclosed is an isolated N-way power divider for operation at high frequencies. The power divider has isolating resistive terminations in the form of transmission line terminations connected to a set of transmission lines. The termination and transmission line arrangement eliminates the need for a set of star connected" resistors characteristic of prior art isolated power dividers,

12 Claims, 6 Drawing Figures PATENTED SEP 9 i975 SHEET 2 BF 3 FIG.

FIG. 3A

PATENTED SEP 91975 sum 3 o 3 mv 6E N-WAY POWER DIVIDER W'ITH REMOTE ISOLATING RESISTORS BACKGROUND OF THE INVENTION This invention relates to isolated power dividers and more particularly to such power dividers designed for use with electrical signals at high frequencies, for example above 100 MHZ.

In various high frequency systems it is often desirable to divide a high frequency signal on one transmission line into a number of substantially identical signals on a like number of transmission lines. This type of signal division may take place as part of an antenna system where it is desirable to supply a portion of the original signal to a number of individual antenna units, in a power amplifier system where it is desired to drive a number of solid state amplifiers with the same signal, or in a cable transmission system wherein the original signal is to be supplied to a selected number of cables.

Among the various devices for accomplishing power division there are "hybrid junctions", directional couplers and power dividers, both isolated and reactive. Directional couplers are commonly used at microwave frequencies for supplying power from an input port to a pair of output ports in a selected power ratio, called the coupling ratio. A coupler has an additional port. which is usually terminated, which is called the isolated port since signals supplied to the input port are not coupled to the isolated port. All of the ports of a directional coupler are impedance matched to their cor responding transmission lines. The output ports of a di' rectional coupler are also mutually isolated. that is, a signal supplied to one output port will not appear at the other output port. but will appear at both the input port and the isolated port. The directional coupler has two inherent disadvantages for use in many power divider applications. First. there is provided only a two-way power division. hence many couplers may be required to achieve a manyavay power split. Second, the signals in the output ports of the directional coupler have a quadrature phase relation, and phase correction is required where it is desired to have equal-phase output signals.

Hybrid junctions are similar to directional couplers in that the two output ports are impedance matched and mutually isolated. Hybrid junctions are different by reason of the fact that the output signals are identical in both amplitude and phase. Hybrid junctions are therefore limited to binary power division and like the directional coupler have only two output ports.

Power dividers have a single input port and two or more output ports. There are two general types of power dividers. commonly known as reactive power dividers" and isolated power dividers." In its usual form a reactive power divider has a single input port and a set of N output ports. Each of the output ports is connected to thc input ports by a quarter-wavelength transmission line which is chosen to have an impedance to match the input port to the collective output impedance of the N output ports. The reactive power dividcr does not have matched or isolated output ports. When a signal is supplied to only one of the output ports a portion of the signal will he reflected and a portion ofthe signal will appear at each of the other output ports as well as at the input port. The device will be matched for signals applied to the output ports only on the condition that signals of equal amplitude and phase be supplied simultaneously to all of the output ports.

The isolated power divider overcomes the deficiencies of the reactive power divider by providing resistive terminations for unequal signals applied to the output ports. These terminations perform the same function as the isolated port on a directional coupler or hybrid junction and enable the output ports to be impedance matched and isolated. In prior art power dividers the resistive terminations usually take the form of resistors star connected to the output ports as is described below. These resistors are usually not capable of dissipating high average power without overheating and because of the star connection arrangement these resistors cannot be conveniently mounted on a conductive heat sink for use with signals of high average power. Further the star connected resistors in a high-frequency power divider must often be located in close proximity to each other, thereby creating additional heating problems in a high power system.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an isolated N-way power divider.

It is a further object of the present invention to provide such a power divider wherein the isolating resistive terminations of the power divider may be remotely located from each other.

It is a still further object of the present invention to provide such a power divider wherein the resistive terminations may be high power transmission-line termi nations.

In accordance with the present invention there is provided an isolated N-way power divider for operation over a selected frequency band. The power divider includes an input port and a set of N-output ports, each comprising first and second output terminals. There is further included a first set of N transmission lines each for coupling wave energy signals from the input port to a corresponding one of the output ports, each of the transmission lines having an electrical length of an odd integral multiple of one-quarter wavelength at a selected frequency within the frequency hand. There is also included a second set of N transmission lines. each comprising a first conductor connected to one of the first output terminals and a second conductor connected to a reference terminal, the reference terminal being common to all of the second conductors in the second set. There is further provided means for terminating each of the transmission lines of the second set of transmission lines to present a substantially resistive impedance between said first output terminal and said reference terminal and means for presenting an open circuit impedance between each of the second output terminals and the reference terminal.

For a better understanding of the present invention, together with other and further objects thereof. reference is had to the following description. taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

BRIEF DESCRIPTION OF THE FIGURES FIG. I is a prior art isolated power divider.

FIG. 2 is a prior art isolated power divider wherein the star connected resistors are remotely located from the output ports.

FIG. 3 is an isolated power divider constructed in accordance with the present invention.

FIG. 3A is a cross-sectional view of the power divider illustrated in FIG. 3.

FIG. 4A is another isolated power divider constructed in accordance with the present invention.

FIG. 4B is a side view of the isolated power divider illustrated in FIG. 4A.

DESCRIPTION OF FIGURES I and 2 (PRIOR ART) FIG. I shows an isolated power divider constructed in accordance with prior art. By way of example, the FIG. I power divider utilizes microstrip transmission line, but it is well recognized in the art that this type of power divider may be constructed using other types of transmission lines including tri plate strip line or coaxial cable. The FIG. 1 power divider is constructed by depositing a printed circuit upon one surface of a dielectric substrate 10. The other surface of the dielectric substrate is covered with conductive material to form a ground plane. The FIG. 1 power divider includes an input port 11 comprising first and second input terminals. The first input terminal is a circular spot of metal deposited on the substrate which may be seen in FIG. 1 and the second input terminal is the conductive ground plane on the other side of substrate which is not shown in FIG. 1. Connection to this type of termi nal is usually facilitated by use of a coaxial connector mounted on the side of substrate 10 having the conductive ground plane. The outer conductor of the coaxial connector is connected to the ground plane while the inner conductor is connected to the input terminal II shown in FIG. 1.

The power divider of FIG. I also has output ports 13a, 13b and I30 which are of the same type as input port 11 and have first and second output terminals similar to the terminals of input port II. Output ports I311, 13!) and 130 are connected to input port II by transmission lines I211. 12b and I20. Transmission lines I2 comprise a first conductor. which is a strip of metal deposited on substrate 10, as shown in FIG. I, and a second conductor which comprises the conductive ground plane on the other side of substrate 10. Transmission lines 12a, 12b and I are selected to be a quarterwavelength in length at a selected frequency within the operating band of the FIG. I power divider. The impedance of these transmission lines I2 is selected so that the transmission lines I2 form a quarter-wavelength transformer between the collective impedance of output ports 13a. 13b and 13c and the impedance of input port II.

Those skilled in the art will recognize that transission lines 12 will also act as a transformer if selected to have a length which is an odd integral multiple ofa quarterwavelength, but transformers of more than one quarter-wavelength tend to operate over relatively narrower frequency bands.

In addition to operating as an impedance transformer. the odd-multiple of quarter-wavelength length of transmission lines 12 results in an odd-multiple of a half-wavelength electrical length for signals coupled between output ports 13 by input port 11. Thus. signals coupled by this path are out-of-phase with signals directly coupled between output ports 13 by star connected resistors 14, described below. The result is isolation between the output ports since these signals tend to cancel.

In order to provide isolation between output ports 13a, 13b and Be there is provided in the FIG. 1 power divider star connected resistors 14a, 14b and 140. Each of these resistors 14 is connected to a corresponding one of the output ports and they are all connected to reference terminal 15. For proper operation of the power divider reference terminal 15 must be at an opened circuit with respect to the ground plane on the other side of substrate 10. Since the other side of substrate 10 is also one of the output terminals of output ports 13a, 13b and 13(- there is provided an opened circuit impedance between reference terminal 15 and the second terminals of output ports 13a, 13b and 13:. This open circuit condition is necessary for the proper operation of the star connected resistors 14 and to provide isolation between the output ports 13 as described above.

FIG. 2 is another prior art isolated power divider. In addition to the elements of FIG. 1 power divider the FIG. 2 power divider has transmission lines 16a, 16b and 16c connected between star connected resistors 14 and output ports 13. These transmission lines are chosen to be approximately one-half wavelength in length so that the impedance of the star connected resistors 14 at terminals 30a, 30b and 30: is presented to corresponding output ports I3. The electrical effect is therefore the same as in the FIG. 1 power divider, but the resistors I4 are located remote from output ports 13.

The FIG. 1 and 2 power dividers have been shown in embodiments of 3-way power dividers for purposes of illustration and the same type of design technique may be used to construct dividers having any number of output ports.

One problem associated with constructing the FIG. I and 2 power dividers at high frequencies is associated with the capability of resistors I4 to handle moderate or high power signals. Since the resistors I4 are star connected. they cannot be conveniently cooled when dissipating high power signals.

DESCRIPTION OF THE INVENTION FIG. 3 shows an isolated N-way power divider constructed in accordance with the present invention wherein the isolating resistive terminations take the form of transmission line terminations. The FIG. 3 power divider has an input port LI, transmission lines 12 and output ports 13 which are substantially identical to the corresponding elements in the prior art power divider of FIG. 1. In the FIG. 3 power divider the star connected resistors 14 have been replaced by a set of three transmission lines 18a. 18b and 180. The transmission lines 18 are in the form of coaxial cables having a first conductor I9, which is the inner conductor and a second conductor which is the outer conductor. The inner conductor 10 of each 19 cable I8 is connected to a corresponding one of the first output terminals of the output ports 13 of the power divider. The outer conductors of the transmission lines 18 are each electrically connected to reference terminal 15', which in the FIG. 3 embodiment is the end of the inner conductor 20 of a transmission line 22. Each of the coaxial cables 18 is terminated in its characteristic impedance. As a consequence, each of these cables is the electrical equivalent of a resistor connected between a corresponding first output terminal 13 and reference termi nal 15'.

Those skilled in the art will recognize that terminating transmission lines 18 in their characteristic impedance result in the desired effect of presenting a resistive impedance between the first output terminals of output ports 13 and reference terminal This result may, of course, be achieved by other than a characteristic impedance load, utilizing appropriate transformer or matching techniques on transmission lines 18.

Transmission line 22 is a coaxial line, selected to have a length *L", which is a quarter-wavelength at a selected frequency within the frequency band and is terminated by a short circuit 24. The result of this short circuited quarter-wavelength transmission line 22 is to present an open circuited impedance between reference terminal 15' and the second terminals of output ports 13 of the power divider. In the FIG. 3 embodiment the second terminals of output ports 13 comprise the conductive ground plane 17 on substrate 10, which is electrically connected to the outer conductor 26 of coaxial output connector 27. The open circuit impedance condition results in reference terminal 15' being the electrical equivalent of reference terminal 15 in the prior art power divider of FIG. 1. The combination of short circuited transmission line 22 and terminated transmission lines 18 is therefore an electrical equivalent of star-connected resistors 14 of the prior art power divider of FIG. I.

The transmission lines 18 of the FIG. 3 embodiment are terminated in transmission line terminations 28a, 28b and 28c, which may be conveniently located remote from each other and from the output ports 13 of the power divider. It may also be seen that since these terminations are of the conventional transmission line type, they may be selected to accommodate a high average power signal and may be cooled by any conventional method used in such terminations, for example, radiation cooling, convection cooling, liquid cooling or conduction cooling to a heat sink. By having this form of isolating resistive termination, the embodiment of FIG. 3 has removed the requirement for star-connected resistors which was a limiting factor to the power capability of the prior art isolated power dividers.

Shown in FIG. 4 is another embodiment of the present invention, which corresponds to the prior art power divider of FIG. 2. The FIG. 4 power divider includes an input port 11, transmission lines 12 and output ports 13 which are similar to the corresponding elements in the prior art power divider of FIG. 2, and the power divider of FIG. 3 described above. The FIG. 4 power divider also has output connectors 27 which are similar to those provided for the FIG. 3 power divider which have their outer conductors connected to ground plane 17. Included in the FIG. 4 power divider are transmission lines 16a, 16b and 16c between output ports 13 and the second set of transmission lines 18. This set of transmission lines 16 is a half-wavelength in length at a selected frequency within the operating frequency band and, as in the FIG. 2 prior art power divider, cause the imp edance presented at terminals 30a, 30b and 30c to be presented to the corresponding output ports 13. Those skilled in the art will recognize that transmission lines 16 may also be any integral multiple of a halfwavelength and still cause the impedances presented at terminals 30 to be presented at output ports 13. The FIG. 4 embodiment is also distinguished from the FIG. 3 embodiment in that the second set of transmission lines 18 is in the form of microstrip, rather than coaxial line, and are terminated in microstrip terminations 28. In this form, one conductor of each of the second set of transmission lines 18 is connected to one terminal of output ports 13 by half-wavelength transmission line 16. The other conductor of transmission lines 18 comprises a conductive ground plane 32, which is connected to reference terminal 15'', which in the FIG. 4 embodiment comprises one edge of ground plane 32. In the FIG. 4 embodiment an open circuit impedance is presented between reference terminal 15" and the ground plane of the terminals 30 by a short circuited parallel plate transmission line formed between conductive ground plane 32 and conductive ground plane 17, having a length L, which is a quarter-wavelength at a selected frequency within the frequency band. This parallel plate transmission line is terminated by short circuit 34.

In the FIG. 4 embodiment the impedance presented to transmission lines 16 at terminal 30 is also presented to output ports 13. The result is the electrical equivalent of the star-connected resistors across output ports 13 of the FIG. 1 prior art power divider. The use of half-wavelength transmission lines I6, as shown in FIG. 4, to separate transmission lines 18 and reference terminal 15" from output ports 13, is most useful in power dividers having many output ports, where physical colocation is difficult.

While the embodiments of the invention which have been described all consist of three-way power dividers, it will be evident to those skilled in the art that such power dividers may be constructed having any number N of output terminals to form an N-way divider. where N is any integer greater than I. It will also be evident that although the present invention is referred to as a power divider," such devices are inherently reciprocal and may also be used as a power combiner and devices intended for such application are within the scope of this invention.

While there have been described what are at present believed to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is, therefore, aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An isolated N-way power divider, where N is an integer greater than one, for operation over a selected frequency band, comprising:

an input port;

a set ofN output ports, each comprising first and second output terminals;

a first set of N transmission lines, each for coupling wave energy signals from said input port to a corresponding one of said output ports, each of said transmission lines having an electrical length of an odd integral multiple of one-quarter wavelength at a selected frequency within said frequency band;

a second set of N transmission lines, each comprising a first conductor connected to a corresponding one of said first output terminals and a second conductor connected to a reference terminal, said reference terminal being common to all of said second conductors in said second set;

means for independently terminating each of the transmission lines of said second set of transmission lines to present a substantially resistive impedance between said first output terminal and said reference terminal;

and means for presenting an open-circuit impedance between each of said second output terminals and said reference terminal.

2. An isolated N-way power divider as specified in claim I wherein each of said transmission lines of said first set of N transmission lines has an electrical length of one-quarter wavelength at a selected frequency within said frequency band.

3. An isolated N-way power divider as specified in claim I wherein said means for terminating each of the transimission lines of said second set of transmission lines comprises means for terminating each of said transmission lines in its characteristic impedance.

4. An isolated N-way power divider as specified in claim 1 wherein said means for presenting an open circuit impedance comprises a shortcircuited transmission line having an electrical length of a quarterwavelength at a selected frequency within said frequency band.

5. An isolated N-way power divider as specified in claim I wherein said second set of transmission lines comprises a set of N coaxial cables. and said first conductor comprises the inner conductor of each of said cables and said second conductor comprises the outer conductor of each of said cables.

6. An isolated N-way power divider as specified in claim l wherein said second set of transmission lines comprises a set of microstrip transmission lines, each comprising a first conductor on a dielectric substrate and a second conductor comprising a ground plane on the opposite side of said substrate, said second conductor being common to all of the transmission lines in said second set.

7. An isolated N-way power divider, where N is an integer greater than one, for operation over a selected frequency band, comprising:

an input port;

a set of N output ports, each comprising first and second output terminals;

a first set of N transmission lines. each for coupling wave energy signals from said input port to a corresponding one of said output ports, each of said transmission lines having an electrical length of an odd integral multiple of one-quarter wavelength at a selected frequency within said frequency band;

a second set of N transmission lines, each comprising a first conductor and a second conductor connectcd to a reference terminal, said reference terminal being common to all of said second conductors in said second set;

a third set of N transmission lines, each having a length which is an integral multiple of a halfwavelength at a selected frequency within said fre quency band, and each comprising a first conductor connected between a corresponding one of said first output terminals and the first conductor of a corresponding one of said second set of transmission lines, and a second conductor connected to a corresponding one of said second output terminals;

means for independently terminating each of the transmission lines of said second set of transmission lines to present a substantailly resistive impedance between said first conductor of said third set of transmission lines and said reference terminal;

and means for presenting an open-circuit impedance between each of said second conductors in said third set of transmission lines and said reference terminal.

8. An isolated N-way power divider as specified in claim 7 wherein each of said transmission lines of said first set of N transmission lines has an electrical length of one-quarter wavelength at a selected frequency within said frequency band.

9. An isolated N-way power divider as specified in claim 7 wherein said means for terminating each of the transmission lines of said second set of transmission lines comprises means for terminating each of said transmission lines in its characteristic impedance.

[0. An isolated N-way power divider as specified in claim 7 wherein said means for presenting an open circuit impedance comprises a short circuited transmission line having an electrical length of a quarterwavelength at a selected frequency within said frequency band.

ll. An isolated N-way power divider as specified in claim 7 wherein said second set of transmission lines comprises a set of microstrip transmission lines, each comprising a first conductor on a dielectric substrate and a second conductor comprising a ground plane on the opposite side of said substrate, said second conductor being common to all of the transmission lines in said second set.

[2. An isolated N-way power divider as specified in claim 7 wherein said third set of transmission lines comprises a set of microstrip transmission lines, each comprising a first conductor on a dielectric substrate and a second conductor comprising a ground plane on the opposite side of said substrate, said second conductor being common to all of the transmission lines in said third set. 

1. An isolated N-way power divider, where N is an integer greater than one, for operation over a selected frequency band, comprising: an input port; a set of N output ports, each comprising first and second output terminals; a first set of N transmission lines, each for coupling wave energy signals from said input port to a corresponding one of said output ports, each of said transmission lines having an electrical length of an odd integral multiple of one-quarter wavelength at a selected frequency within said frequency band; a second set of N transmission lines, each comprising a first conductor connected to a corresponding one of said first output terminals and a second conductor connected to a reference terminal, said reference terminal being common to all of said second conductors in said second set; means for independently terminating each of the transmission lines of said second set of transmission lines to present a substantially resistive impedance between said first output terminal and said reference terminal; and means for presenting an open-circuit impedance between each of said second output terminals and said reference terminal.
 2. An isolated N-way power divider as specified in claim 1 wherein each of said transmission lines of said first set of N transmission lines has an electrical length of one-quarter wavelength at a selected frequency within said frequency band.
 3. An isolated N-way power divider as specified in claim 1 wherein said means for terminating each of the transimission lines of said second set of transmission lines comprises means for terminating each of said transmission lines in its characteristic impedance.
 4. An isolated N-way power divider as specified in claim 1 wherein said means for presenting an open circuit impedance comprises a short-circuited transmission line having an electrical length of a quarter-wavelength at a selected frequency within said frequency band.
 5. An isolated N-way power divider as specified in claim 1 wherein said second set of transmission lines comprises a set of N coaxial cables, and said first conductor comprises the inner conductor of each of said cables and said second conductor comprises the outer conductor of each of said cables.
 6. An isolated N-way power divider as specified in claim 1 wherein said second set of transmission lines comprises a set of microstrip transmission lines, each comprising a first conductor on a dielectric substrate and a second conductor comprising a ground plane on the opposite side of said substrate, said second conductor being common to all of the transmission lines in said second set.
 7. An isolated N-way power divider, where N is an integer greater than one, for operation over a selected frequency band, comprising: an input port; a set of N output ports, each comprising first and second output terminals; a first set of N transmission lines, each for coupling wave energy signals from said input port to a corresponding one of said output ports, each of said transmission lines having an electrical length of an odd integral multiple of one-quarter wavelength at a selected frequency within said frequency band; a second set of N transmission lines, each comprising a first conductor and a second conductor connected to a reference terminal, said reference terminal being common to all of said second conductors in said second set; a third set of N transmission lines, each having a length which is an integral multiple of a half-wavelength aT a selected frequency within said frequency band, and each comprising a first conductor connected between a corresponding one of said first output terminals and the first conductor of a corresponding one of said second set of transmission lines, and a second conductor connected to a corresponding one of said second output terminals; means for independently terminating each of the transmission lines of said second set of transmission lines to present a substantailly resistive impedance between said first conductor of said third set of transmission lines and said reference terminal; and means for presenting an open-circuit impedance between each of said second conductors in said third set of transmission lines and said reference terminal.
 8. An isolated N-way power divider as specified in claim 7 wherein each of said transmission lines of said first set of N transmission lines has an electrical length of one-quarter wavelength at a selected frequency within said frequency band.
 9. An isolated N-way power divider as specified in claim 7 wherein said means for terminating each of the transmission lines of said second set of transmission lines comprises means for terminating each of said transmission lines in its characteristic impedance.
 10. An isolated N-way power divider as specified in claim 7 wherein said means for presenting an open circuit impedance comprises a short circuited transmission line having an electrical length of a quarter-wavelength at a selected frequency within said frequency band.
 11. An isolated N-way power divider as specified in claim 7 wherein said second set of transmission lines comprises a set of microstrip transmission lines, each comprising a first conductor on a dielectric substrate and a second conductor comprising a ground plane on the opposite side of said substrate, said second conductor being common to all of the transmission lines in said second set.
 12. An isolated N-way power divider as specified in claim 7 wherein said third set of transmission lines comprises a set of microstrip transmission lines, each comprising a first conductor on a dielectric substrate and a second conductor comprising a ground plane on the opposite side of said substrate, said second conductor being common to all of the transmission lines in said third set. 